Laser beam irradiance adjustment and control can be difficult to achieve over an irradiance range of one order of magnitude or more. Even within this range, the accuracy and stability in the irradiance of the light output from a typical laser is often suboptimal for certain applications. Typical solutions for controlling the irradiance of a laser include controlling the current applied to the source or placing neutral density filters in the laser beam path to reduce the beam irradiance. In recent years, laser shutters have been optimized for speed by reducing the size of the shutters and by increasing the electrical power used to the control the shutters. As a result, laser shutters can be placed in the laser beam path to turn the laser beam “on” and “off.”
However, current control, density filtering, and use of shutters to adjust and control the irradiance of a laser beam is not optimal, especially when adjusting the laser on the sub-millisecond time scale is desired. For instance, the response time of a laser to a linearly controlled power source is typically non-linear, which limits the range of adjustability to about one order of magnitude. In addition, the temperature of a typical laser may fluctuate during operation, resulting in further irradiance instability. Neutral density filters may improve the irradiance range by several orders of magnitude, but filters provide only coarse irradiance adjustment, and typical high speed shutters are not capable of achieving sub-millisecond open and close times despite the reduced size of the aperture and higher driving voltages. For the above described reasons, engineers and scientists who develop and work with instruments that relay on high-speed control of laser light irradiance continue to seek mechanisms for laser beam irradiance adjustment and control on the sub-millisecond time scale.